1. Field of the Invention
The present invention relates to an apparatus for growing a silicon ingot and, more particularly, to an apparatus in which the driving axis of a graphite crucible is modified.
2. Background of the Related Art
A perfect wafer is necessary for fabricating a highly-integrated circuit device in accordance with the development of semiconductor circuit devices. In order to produce such a high-quality silicon wafer, a high-quality single crystalline silicon ingot is required as well. In known apparatuses for growing a single crystalline silicon ingot, a Czochralski growth method is widely used.
A growth apparatus according to a related art, as shown in FIG. 3, includes a graphite crucible 33 into which a quartz crucible 32 containing a molten silicon 34 is placed. A driving axis 36 is connected to a lower part of the graphite crucible 33 to revolve and to move the graphite crucible up and down so as to support the graphite crucible 33. A heating means 35 heats the graphite crucible 33, and an outer chamber 38 having an insulating wall 37 protects and thermally isolates the graphite crucible 33, heating means 35, and driving axis 36 in part from an external environment. The dotted lines indicate isothermal lines for marking a temperature distribution.
Such an apparatus for growing a single crystalline silicon ingot 31 according to the related art uses the driving axis as shown in FIG. 1. An upper axis of the driving axis 10 is manufactured by processing a graphite pillar, in which a cave 11 is formed at the upper part of the driving axis 10 and a support 12 is formed to be coupled with the graphite crucible 33. The lower part 13 of the driving axis is formed cylindrically so as to be coupled with a rotating means as well as an elevating means (ex. cylinder) to move up and down.
The driving axis of the single crystalline growth apparatus plays the role of supporting, revolving, and moving upward/downward a crucible into which molten silicon is placed. A crystal growth system, which uses a driving axis designed for producing a simple revolution, depends on a fast heat transfer occurring at a place where the driving axis and a cooling system in a chamber are adjacent each other, thereby bringing about instability due to environmental variance. Moreover, a temperature gradient in the molten silicon supported by the driving axis becomes wider due to the heat loss through the driving axis, thereby degrading the quality of crystals.
The growth apparatus having such a driving axis according to the related art, as shown in FIG. 3, brings about excessive heat loss through the driving axis when a single crystalline silicon is grown, thereby widening the temperature gradient inside the silicon melting pot. The temperature gradient, which is directly reflected in the quality of the growing single crystalline silicon, is a major issue for process management. Moreover, heat flux through the driving axis reduces thermal efficiency as well.
Accordingly, the present invention is directed to an apparatus for growing a silicon ingot that substantially obviates one or more of the problems that arise due to limitations and disadvantages of the related art.
An object of the present invention is to provide an apparatus for growing a silicon ingot which is able to improve a quality of a single crystalline ingot by alleviating the temperature gradient in the molten silicon through improvement of the driving axis of the silicon growing apparatus.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, an apparatus for growing a silicon ingot according to the present invention includes a graphite crucible in which a quartz crucible is placed, a driving axis connected to a lower part of the graphite crucible to revolve and move the graphite crucible up and down so as to support the graphite crucible, a heating means to heat the graphite crucible, and an insulating wall to protect and thermally isolate the graphite crucible, heating means, and driving axis in part from the external environment. The driving axis includes a hollow axis part having a hollow interior, an insulating axis part attached to the bottom of the hollow axis part to inhibit heat transfer, and a cylindrical axis part attached to the bottom of the insulating axis part.
Preferably, the insulating axis part is designed to lie at a position corresponding to the insulating wall when the driving axis moves upward and downward and is formed of an anisotropic insulator.
Preferably, the insulating axis part is formed of a plurality of anisotropic insulator discs stacked successively.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.